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Old 04-06-2012, 10:14 PM   #1
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Default Wanting to go 3s

I would not call my self a noob to rc but it is a hobby of mine . I dont get to mess with it much but have been into it for years. On to the point , i have been wanting to switch to 3s lipos . I have ran 2s for a few years i understand mah ratings and all that junk but my ? is other than power will say for example a 3300mah 3s lipo have around the same run time as a 3300mah 2s lipo ? I only ask because more power same size and weight should make the truck move easier therefore last longer ? This is where iam not so sure . Any Help is great as always
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Old 04-06-2012, 10:30 PM   #2
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Default Re: Wanting to go 3s

Quote:
Originally Posted by Butcherinhd View Post
I would not call my self a noob to rc but it is a hobby of mine . I dont get to mess with it much but have been into it for years. On to the point , i have been wanting to switch to 3s lipos . I have ran 2s for a few years i understand mah ratings and all that junk but my ? is other than power will say for example a 3300mah 3s lipo have around the same run time as a 3300mah 2s lipo ? I only ask because more power same size and weight should make the truck move easier therefore last longer ? This is where iam not so sure . Any Help is great as always
Should be similar, capacity is a function of parallel connections not series so the battery has 3300mah capacity on each cell and it is not dependent of the number of cells in series. Both cells in a 2s pack each have 3300mah capacity and all 3 in a 3s pack have 3300mah of capacity etc.

Now if you wired two packs in parallel then the voltage would remain the same but you would add the capacity of the two packs together so you would get increased runtime.

Im not an expert in electrical efficiency though so Im not sure if you would get longer or shorter runtime based on increased or decreased efficiency of the system so that may play a role in this. I would think that it would be similar enough that you would not notice a difference...minus the increase in power!
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Old 04-06-2012, 10:57 PM   #3
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Default Re: Wanting to go 3s

Thats what i was thinkin as well. Thanks for the input
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Old 04-07-2012, 12:31 PM   #4
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Default Re: Wanting to go 3s

A 2s 3300mah pack should give you 24.42 Watt-hours of energy (7.4v x 3.3amp-hours) whereas a 3s 3300mah pack should give you 36.63 Watt-hours of energy (11.1v x 3.3amp-hours)
Provided you are running the same speed, using the same power, you could in fact have a 50% longer runtime.
That's only if you gear down to the same speed as you were on 2s.
To find out how much lower you need to gear down, just think of it as right now you are running two thirds of the voltage you want to run, so when you get the 3s battery you will need a pinion two thirds the size you have now to get the same speed.
If you keep the same pinion and drive WOT all the time, then you will just end up with a higher top end and the same runtime.
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Old 04-07-2012, 08:38 PM   #5
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Default Re: Wanting to go 3s

Correct, go by the stored energy (24Whours vs. 36). Also a good help when you are shopping around for batteries, check the price per Wh for a comparison.
More things to consider:
1) your ESCs will typically be built for 6-7 cell NiCd (back then) so you probably will need a new one that can handle 3s (11.1V)
2) as long as you keep the same top speed, aka gear down, the current will drop, you can go down in wire diameter (or up in gauge)

cheers

braq

PS: I have switched all rigs above 4 lbs to 3s
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